Federal regulations prevent the use of a burner which ignites more than one million BTU's of fuel at one time. Consequently, if a burner utilizes more BTUs than that, then some other method must be utilized to comply with such Federal regulations. The reason for such a requirement is that if too much fuel is lit at one time, it is likely to explode the entire fuel chamber once it is lit. Consequently, certain motorized fuel valves have been utilized to light a low number of BTUs initially and then to increase the flow of fuel and air through such burner until such time that the needed BTUs are achieved.
While such a system is functional, it is not ideal and is more expensive and complicated to use than the situation where no motorized valves are required.